Development of a coaxial extrusion deposition for 3D printing of customizable pectin-based food simulant

A coaxial extrusion printhead was designed for 3D printing of pectin-based food simulants in which the inner flow is the food-ink and the outer a CaCl2 crosslinking solution. A series of cubic-shaped objects was successfully 3D printed by changing the printing parameters including the food-ink composition, the layer height, and the rate and CaCl2 concentration of the outer flow. The printed objects did not necessitate any incubation post-treatment because the gelation of the food-ink occurred during the printing. The mechanical properties of the printed object were correlated to their final Ca2+ concentration which can be controlled by the rate and CaCl2 concentration of the outer flow. A predictive model was established for determining the printing settings to print 3D objects with a priori defined texture. The layer height was recommended to be set in function of the food-ink swelling behavior. Finally, we compared objects printed by coaxial and simple extrusion methods. The compared objects had similar Young's moduli but their other properties including volume and final Ca2+ concentration, were considerably impacted by the printing method.status: publishe

Contrast enhanced imaging of food microstructure with X-Ray microCT

The ability to acquire images of intact microstructures of food products is of great benefit to both structural and functional studies related to food processing and preservation. X-Ray microCT is particularly well suited for this purpose as it benefits from both its nondestructive nature as well as the high resolution output. However, fundamental limitation of X-rays results in the inability of CT systems to distinguish between materials with similar atomic composition. In the context of food microstructure studies, this results in the inability to separate otherwise distinctive structures such as dense cell clusters in tissues of fruit or meat. While the medical imaging field have been developing and utilizing contrast agents to combat this limitation, these agents are seldom used outside of medicine. This study explores and demonstrates the value of utilizing contrast enhancing agents for purposes of both cell cluster separation and structure labelling. With the use of commercially available contrast enhancing agents in conjunction with optimized delivery methods, we demonstrate the significant improvement in both cellular and structural separation of both fruit and meat tissue samples. The enhanced separation allows additional software processing in which more accurate 3D models of intact structures can be produced, and thus provide a better foundation for downstream analysis and modeling.status: publishe

3D printing of plant tissue for innovative food manufacturing: encapsulation of alive plant cells into pectin based bio-ink

3D food printing allows creation of foods by depositing food material according to computer aided designs. However, the number of printable materials for food is still low which limits the possibilities of creating specific structures and textures. A novel approach is tested of using food printing materials incorporating plant cells in order to print foods that resemble plant tissues in various ways. A 3D printing method was developed based on the extrusion of bio-inks composed of a low-methoxylated pectin gel and embedded lettuce leaf cells. Bovine serum albumin was added in order to increase the air fraction in the printed gel matrix. Objects containing up to 5 × 106 cells/mL were successfully 3D printed. The mechanical strength increased by the pectin concentration and decreased with the increase of air fraction and concentration of encapsulated cells. The viability of the encapsulated plant cells depended on the pectin concentration and varied from 50 to 60 %.status: accepte

Model-based design and validation of food texture of 3D printed pectin-based food simulants

A prime interest in 3D food printing consists of controlling the texture of food products by means of structure design. Analytical and finite element models were used to predict the texture properties of printed honeycomb structures. Structures with varying cell size were 3D printed using food-inks composed of three different pectin concentrations and characterized with micro-CT and compression analysis. Porosity and average wall thickness of the samples appeared independent of food-ink composition but structure deviations could be distinguished between actual printed structures and CAD designs. The comparison between the texture properties of printed structures and those predicted by analytical and FE modelling in function of porosity showed that both predicted and actual texture properties matched to the same decreasing trend with increasing porosity. Finally, a good fit of the analytical model to the measured Young's modulus was obtained by using the actual porosity of the printed structures, while the validated finite element model provides a means to design more complex structures. The results emphasize the importance of structure correspondence for reliable design of texture properties of printed food structures.status: Published onlin

Structural-mechanical analysis of cookies produced by conventional and 3D printing techniques

Little knowledge exists of the relationship between mechanical properties and microstructure of cookies. A cookie can be described as a solid matrix in which gas spaces of different sizes and shapes are embedded. Additive manufacturing or 3D printing has emerged as a novel method to produce cookies. The process of 3D printing is, however, significantly different from a conventional baking process. In order to assess the texture of 3D printed cookies relative to that of traditional cookies, in this study the mechanical and structural properties of cookies of different compositions and production methods were measured and analysed. Three-point bending tests were performed to determine Young’s modulus, failure stress and strain. X-ray micro-CT imaging at 5 µm pixel size was applied to characterise the 3D microstructure of the cookie samples used in mechanical testing. Of the microstructure properties, structure thickness distribution appeared to change Young’s modulus of cookies; which could be affected by the sugar and fat composition in traditional cookies. The structure of printed cookies strongly depended on both the printing method and the composition. Both particle size of the flour and the binder composition were significant. The structure: binder ratio was less effective to change structure. The final aims of this study are to combine knowledge to understand structure-property relationships of cookies incorporating observed structural properties and to construct a model capable of computing mechanical properties of foods from the microstructure and composition.status: publishe

Structure design of 3D printed cookies in relation to texture

In order to develop a model that allows for a better understanding of the interaction between the properties of the solid matrix, the structure and the mechanical behaviour of the cookie, both mechanical and structural properties need to be taken into account. To this end, a finite element model (FEM) was developed that predicts the mechanical properties of the structured product based on the material properties of the solid material used. The solid material mechanical properties were measured using compression tests with a universal testing machine. A larger variation of structures was analysed by means of FEM simulations, varying the size and shape of the air spaces and wall thickness of the structure. Structural parameters such as porosity, pore size and wall thickness were correlated to the mechanical properties such as Young’s modulus. In a next step these structures validated by means of mechanical compression tests on actual printed structures (by means of fused deposition modelling) with different air space distributions based on the 3D FE design files. The structure of the printed cookies will also be verified by means of 3D micro-CT imaging. Using this final correlation model, microstructure of the products can be engineered to achieve desirable texture properties in silico and create dedicated print files for additive manufacturing of cookies.status: publishe

Pectin Based Food-ink Formulations for 3-D Printing of Customizable Porous Food Simulants

Additive manufacturing is revolutionizing processing in many applications including 3-D food printing. So far the number of suitable printable materials for food is limited and the microstructure and texture properties of 3-D printed food have been characterized poorly. This study introduces the novel concept of customizable water-based porous food simulants by 3-D printing using low methoxylated pectin gel as food-ink. A series of pectin gels was successfully 3-D printed by changing the formulation parameters including stirring rate and pectin, CaCl2, bovine serum albumin and sugar syrup concentrations. It was shown that food objects with variable microstructure and texture properties can be 3-D printed by using different pectin based food-inks. The pectin concentration was the main determinant of firmness and strength of the printed object. Sugar and pectin concentrations increased viscosity and affected the build quality. BSA stabilized and promoted the aeration of the food-ink. This resulted in a pore size distribution after printing that was influenced by the viscosity of the food-ink. A predictive model was established for designing the food-ink composition to obtain 3-D printed food simulants with a priori defined microstructure and texture.status: publishe

Designing Mechanical Properties of 3D Printed Cookies through Computer Aided Engineering

Additive manufacturing or 3D printing can be applied in the food sector to create food products with personalized properties such as shape, texture, and composition. In this article, we introduce a computer aided engineering (CAE) methodology to design 3D printed food products with tunable mechanical properties. The focus was on the Young modulus as a proxy of texture. Finite element modelling was used to establish the relationship between the Young modulus of 3D printed cookies with a honeycomb structure and their structure parameters. Wall thickness, cell size, and overall porosity were found to influence the Young modulus of the cookies and were, therefore, identified as tunable design parameters. Next, in experimental tests, it was observed that geometry deformations arose during and after 3D printing, affecting cookie structure and texture. The 3D printed cookie porosity was found to be lower than the designed one, strongly influencing the Young modulus. After identifying the changes in porosity through X-ray micro-computed tomography, a good match was observed between computational and experimental Young’s modulus values. These results showed that changes in the geometry have to be quantified and considered to obtain a reliable prediction of the Young modulus of the 3D printed cookies

Designing Mechanical Properties of 3D Printed Cookies through Computer Aided Engineering.

Additive manufacturing or 3D printing can be applied in the food sector to create food products with personalized properties such as shape, texture, and composition. In this article, we introduce a computer aided engineering (CAE) methodology to design 3D printed food products with tunable mechanical properties. The focus was on the Young modulus as a proxy of texture. Finite element modelling was used to establish the relationship between the Young modulus of 3D printed cookies with a honeycomb structure and their structure parameters. Wall thickness, cell size, and overall porosity were found to influence the Young modulus of the cookies and were, therefore, identified as tunable design parameters. Next, in experimental tests, it was observed that geometry deformations arose during and after 3D printing, affecting cookie structure and texture. The 3D printed cookie porosity was found to be lower than the designed one, strongly influencing the Young modulus. After identifying the changes in porosity through X-ray micro-computed tomography, a good match was observed between computational and experimental Young's modulus values. These results showed that changes in the geometry have to be quantified and considered to obtain a reliable prediction of the Young modulus of the 3D printed cookies.status: Published onlin